This invention relates to an apparatus for working on work material wherein a table has a work material support surface selected areas of which may be vacuumized, and deals more particularly with an improved valving system for such a table, in means for operating such valving system to obtain a desired mode of operation, and in the combination of such valving system with a bristle bed of such table to achieve a desired application of the vacuum to the work material.
Apparatus embodying this invention may be used in many different applications where it is necessary or desirable to have a work material supporting surface selected areas of which may be vacuumized for various purposes. An especially advantageous application of the apparatus is in the textile or upholstery industry where one or more layers of fabric or other sheet material are spread onto a work surface for subsequent cutting or other processing. It may for example be desirable as the sheet material is spread by a spreader onto the work surface to successively vacuumize different transversely extending sections of the work table, in keeping with the movement of the spreader, so that the area of the table at which the sheet material passes from the spreader to the table, and only that area, is subjected to a vacuum to aid in smoothly applying the sheet material to the table. In another case selected areas of the work table may be vacuumized to aid in fixing the layer or layers of sheet material to the table, and also possibly to compress such layer or layers, with or without the use of an overlying air-impermeable sheet, while the layer or layers are cut with the selected area of the work surface subjected to vacuum being one underlying a cutting tool which moves over the work surface. In this case, as the tool moves longitudinally of the work surface different transverse zones or areas are vacuumized and devacuumized in keeping with the movement of the tool, and it is desirable that the degree of vacuum be greatest at the transverse area directly underlying the tool and that the vacuum gradually taper off to zero, as a function of distance from the tool, on either side of the tool longitudinally of the table. It is also desirable in this case as different transverse areas of the work surface become vacuumized and devacuumized, as a result of movement of the tool longitudinally of the work surface, that such vacuumization and devacuumization occur gradually and without any sudden surges as might adversely disturb the sheet material on the work surface.
The ability to vacuumize only an area of the work support surface located in the vicinity of the cutting tool has various benefits, a principal one of which is the ability generally of being able to operate the table with a much less powerful vacuum source than would be required for applying a vacuum over the entire work surface. This is especially true where a layup of sheet material to be cut is covered with an air-impermeable sheet as part of a vacuum holddown means. If vacuum is applied over the entire work surface, before any cutting takes place, the air-impermeable sheet serves as an air seal so that only a relatively low demand is put on the vacuum source. However, as the cutting progresses the cuts made by the cutter in the layup and in the overlying air-impermeable sheet allow air to move through the layup into the vacuum system putting a load on the vacuum source which increases as more and more cuts are made. Also, if the table is used for holding only a single layer, or a few superimposed layers, of air-permeable work material without the use of an overlying air impermeable sheet, if the whole support surface is vacuumized much air will pass into the vacuum system through the work material and require a large capacity vacuum source to maintain a desirable vacuum level at the work support surface. Therefore, in both these cases vacuumizing only a small area of the work support surface obviously reduces the maximum load imposed on the vacuum source and allows a less powerful and more inexpensive one to be used.
The basic idea of applying a vacuum to only a selected area of a work surface, and in making such selection in accordance with the position of a tool or carriage relative to the work surface, is old in the art and shown for example by prior U.S. Pat. No. 3,495,492, of which Applicant is a co-inventor. The present invention relates to further implementations of and improvements in that basic idea.
A general object of the invention is therefore to provide an apparatus with a selectively vacuumizable work material support surface of generally similar principle to that of prior U.S. Pat. No. 3,495,492, but having an improved, less expensive, and more efficient and reliable valving system than previously available in the prior art.
Another object of the invention is to provide an apparatus of the foregoing general characteristics wherein the vacuum applied to the work surface, particularly when supporting one or a few layers of air permeable web material without an air impermeable sheet, has a gradient whereby the degree of vacuum is highest in the immediate vicinity of the tool or carriage and gradually diminishes on opposite sides of the tool or carriage longitudinally of the work surface.
Still another object of the invention is to provide an apparatus of the foregoing character wherein the vacuumization and devacuumization of the different transverse areas of the work surface occur gradually without sudden surges.
Where the selective vacuumization of various areas of a work material supporting surface is controlled by the position of a work tool relative to the work surface it is often desirable that the control of the vacuum valving system impose substantially no additional load on or weight to the tool or its positioning mechanism so that the tool may be driven at as high accelerations and decelerations as possible. A further object of the invention is therefore the provision of an apparatus of the foregoing character wherein the valving system is controlled in response to the position of a tool or tool carriage relative to the work surface without adding a significant demand onto the tool positioning system.
Also, in some apparatuses having a selectively vacuumizable work support surface it may at times be desirable to apply a positive air pressure over the entire work support surface instead of a vacuum over only a portion of the surface. This may be of benefit, for example, where the apparatus is a cloth cutting machine where vacuum is used to hold the material to the work support surface during cutting and where after cutting positive pressure is applied over the entire work support surface to create an air cushion between the support surface and the work material to aid in removing the cut material from the work surface and also possibly to aid in bringing a fresh supply of material onto the surface. Therefore, another object of this invention is to provide an apparatus of the foregoing character wherein a positive air pressure may be created over the entire work support surface by simply applying a positive air pressure, instead of a vacuum, to the air plenum.
Other more detailed objects and advantages of the invention will become apparent from the accompanying detailed description of a preferred embodiment taken in conjunction with the accompanying drawings.